In recent years, with the development of information communication technology, the realization of a ubiquitous society is proposed in which free communication of information and a variety of services can be achieved by connecting a variety of electronic devices to a computer network. The word “ubiquitous” comes from the Latin meaning “existing or being everywhere” (being omnipresent) and means that the processing of information using computers is naturally widespread throughout a living environment through electronic devices without any awareness of computers at anytime and anywhere.
In order to make an electronic device operate, power needs to be supplied to the electronic device (hereinafter, also referred to as power feeding). Power is supplied to a portable electronic device typified by a mobile phone and the like by a built-in battery. The battery is charged in the following manner: the electronic device is set in a battery charger and power is received from a commercial power supply distributed to each house. In addition, a contact needs to be provided to connect the electronic device and the battery charger; however, a non-contact power supply method utilizing electromagnetic induction phenomenon which does not need a contact is known because a malfunction due to a contact defect is prevented, a design to which waterproof function is imparted is easily made, and the like.
If positioned alignment of a power feeding side and a power receiving side is not doned accurately in charging by electromagnetic induction, efficient power supply has been difficult; however, in recent years, a sheet-like power supply device has been known in which the power supply efficiency is improved in such a manner that a plurality of power feeding coils are arranged to have a sheet-like shape and power is supplied from only a power feeding coil over which an electronic device which receives power is placed (Non-Patent Document 1).
By supplying power using a radio signal made by electromagnetic induction, the electronic device can be made to operate without consideration of a power supply cord, a position of an outlet, and the like. A power feeding coil functions as an antenna for supplying power using a radio signal.